Apparatus for checking tyres

ABSTRACT

Apparatus for checking a tyre having: a support plane; a deformation element to generate a deformed surface portion; a positioning actuator to move the deformation element; and a device with a camera, a first light source, a second light source, a processing unit and a drive and control unit. The processing unit is programmed to activate the positioning actuator to move the deformation element towards the tyre to generate a deformed surface portion. The drive and control unit is programmed to: actuate the first light source to illuminate the deformed surface portion of the tyre, the second light source being inactive during the deformation; control the camera to acquire a first image of the deformed surface portion; actuate the second light source to illuminate an undeformed surface portion of the tyre; and control the camera to acquire a second image of the undeformed surface portion.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/780,602 filed on May 31, 2018, which in turn is a U.S.National Stage of International Patent Application No. PCT/IB2016/057712filed on Dec. 16, 2016 which, in turn, claims priority to ItalianApplication No. UB2015A009501 filed on Dec. 16, 2015 the contents of allof which are incorporated herein by reference in their entireties.

Typically, a tyre has a substantially toroidal structure about arotation axis thereof during operation, and has an axial mid-planeperpendicular to the rotation axis, said plane typically being a planeof substantial geometric symmetry, ignoring possible minor asymmetries,such as the tread pattern and/or the internal structure.

Two portions of the tyre are identified here: the crown and the sidewalls. The crown comprises the tread band, the belt and thecorresponding portion of carcass structure radially inside them.

The term “side wall” is meant to indicate one of the two portions of thetyre facing one another and that extend radially on opposite sides ofthe crown up to the beads, i.e. up to the two radially inner end edgesof the tyre, having circular extension substantially perpendicular tothe rotation axis; said beads being intended to each couple with arespective mounting rim. Each side wall thus comprises a correspondingportion of carcass structure and, in a position axially outside of it, aportion made of suitable elastomeric material, generally called‘sidewall’.

Typically, the carcass structure comprises at least one carcass plyhaving respectively opposite end edges engaged with respective annularreinforcing structures, generally called “bead wires”, integrated in theareas identified above with the name beads. In “tubeless” tyres, thecarcass ply is entirely coated with a layer of elastomeric materialpreferably butyl-based, usually called “liner” having excellentcharacteristics of impermeability to air and extending from one bead toanother.

The structure of a side wall is also meant to entirely include theso-called “shoulder”, i.e. the portion of the tyre for joining betweenthe crown and the radially inner portion of the side wall (in otherwords, the two shoulders correspond to the two radially and axiallyouter circular ‘edges’ of the tyre). The shoulder has circular extensionsubstantially perpendicular to the rotation axis.

The term “tyre” is meant to indicate the finished tyre, i.e. after themoulding and vulcanisation steps following the building step.

The term component of the tyre is meant to indicate any element thatperforms a function, or a portion thereof.

The terms outer or inner surface of the tyre, are respectively meant toindicate the surface that remains visible after the coupling of the tyrewith its mounting rim and that which is no longer visible after saidcoupling.

The terms “optical”, “luminous” and similar refer to an electromagneticradiation used that has at least one portion of the spectrum fallingwithin a widened range of the optical band, and not necessarily fallingstrictly within the optical band (in other words 400-700 nm), forexample such a widened range of the optical band can extend fromultraviolet to infrared (for example wavelengths comprised between about100 nm and about 1 μm).

In the present application a ray model of light radiation is adopted,i.e. it is presumed that light radiation incident on a point of asurface and generated by a non-pointed source (in which case there wouldbe a single ray) corresponds to a set of light rays incident on thepoint and having rectilinear propagation direction that connects eachpoint of the source with said point of the surface, where each of suchrays has an associated fraction of the total light power incident on thepoint. The terms “light” and “light radiation”, unless specifiedotherwise, are used interchangeably.

The term “directional light radiation” incident at a point of a surfaceis meant to indicate light radiation for which there is a solid anglehaving the point as vertex and amplitude less than or equal to Tr/8steradians in which at least 75% of the total light power, preferably atleast 90%, more preferably the entire light power falls.

The term “diffused light radiation” is meant to indicate anon-directional light radiation.

The term “grazing light radiation” incident at a point of a surface ismeant to indicate a light radiation in which at least 75% of the totallight power thereof incident on the point of the surface forms an angleof incidence less than or equal to 60° with a plane tangent to thesurface at each said point.

The term “image” or synonymously “digital image” is meant to indicate ingeneral a dataset, typically contained in a computer file, in which eachcoordinate (typically two-dimensional) of a finite set (typicallytwo-dimensional and of the matrix type, i.e. N rows×M columns) ofspatial coordinates (each typically corresponding to a pixel) isassociated with a corresponding set of numeric values (which can berepresentative of magnitudes of a different type). For example, inmonochromatic images (like those on the ‘grayscale’) such as set ofvalues coincides with a single value in a finite scale (typically with256 levels or tones), such a value for example being representative ofthe level of luminosity (or intensity) of the respective spatialcoordinate when visualised, whereas in colour images the set of valuesrepresents the level of luminosity of multiple colours, or channels,typically the primary colours (for example in the RGB colour model red,green and blue, whereas in the CMYK colour model cyan, magenta, yellowand black). The term ‘image’ does not necessarily imply the actualvisualisation thereof.

Every reference to a specific “digital image” (for example to atwo-dimensional digital image initially acquired on the tyre) moregenerally covers any digital image that can be obtained through one ormore digital processing operations of said specific digital image (likefor example filtering, equalisation, “thresholding”, morphologicaltransformations—“opening”, etc.,—gradient calculations, “smoothing”,etc.).

The term “linear surface portion” is meant to indicate a surface portionhaving one dimension much larger than the other dimension perpendicularto it, typically greater by at least two orders of magnitude. Thesmaller dimension of the linear surface portion is typically smallerthan or equal to 0.1 mm.

The term “linear image” is meant to indicate a digital image having amuch greater number of columns of pixels than the number of rows,typically greater by at least two orders of magnitude. Typically, thenumber of rows is between 1 and 4 and the number of columns is more than1000. The term “rows” and “columns” are used conventionally and areinterchangeable.

The term “cycle time” within a production line comprising at least onework station, preferably a plurality of work stations, and inserted in aplant for producing tyres is meant to indicate, under normal operatingconditions, the maximum transit time for a tyre being manufactured topass through a work station in which at least one portion of a componentof the tyre itself is built. For example, the cycle time can becomprised between about 20 and about 120 seconds.

In processes for producing and building tyres for vehicle wheels thereis a need to carry out quality controls on the products made, with thepurpose of avoiding tyres that are defective or in any case outside ofthe design specifications from being able to be released onto themarket, and/or of progressively adjusting the apparatuses and machineryused, so as to improve and optimise the performance of the operationscarried out in the production process.

Such quality controls include for example those carried out by humanoperators who spend a predetermined time period, for example comprisedbetween 30 s and 60 s, carrying out a visual and tactile examination ofthe tyre; if, in light of his/her experience and sensitivity, theoperator suspects that the tyre does not meet certain quality standards,the tyre itself is subjected to further checks, through a more detailedhuman check and/or suitable apparatuses, in order to more deeplyevaluate possible structural and/or quality deficiencies.

WO 2015/004587 to the same Applicant shows a method and relativeapparatus, for checking tyres in a production line, comprising:providing a tyre to be checked; elastically deforming a portion of sidewall of the tyre through a compression force on an outer contact surfaceof the portion of side wall, the compression force having an axialdirection and going towards the plane of the middle line; illuminatingan inner and/or outer surface of the portion of side wall and detectingan image of the surface illuminated; generating a control signalrepresentative of the image detected; and analysing the control signalin order to detect the possible presence of defects on the portion ofside wall.

EP 2322899 describes a method for detecting minute irregularities on thesurface of a tyre under inspection. A surface in the region of side wallof a tyre is illuminated by a red light emitted by first illuminationmeans arranged in the direction of 45 degrees with respect to the linenormal to the surface. At the same time, the surface is illuminated by ablue light coming from second illumination means arranged in a directionof −45 degrees with respect to the normal line. The illuminated surfaceis captured by a linear camera from the direction of the normal line.The surface irregularity formed on the surface of the tyre is detectedbased on the waveforms of luminance distribution.

US 2011/018999 shows a device for evaluating the appearance of thesurface of a tyre comprising a linear colour camera including means forseparating the beam of light reflected by the surface of said tyre andentering into the camera into at least two primary colours (R, G, B) ofcertain wavelengths, so as to direct the beam of light to as manysensors capable of obtaining a base image in grayscale for each of theprimary colours, a number of illumination means equal to the number ofprimary colours, said illumination means being oriented so as toilluminate the surface to be evaluated at different angles,characterised in that each illumination means emits a coloured light (R,G, B) different from that emitted by the other illumination means, thewavelength of which substantially corresponds to the wavelength of oneof the primary colours selected by the camera.

In the field of the checking of tyres, the Applicant has set itself theproblem of analysing the surface, inner and/or outer, of the tyre,through optical image acquisition, for example digital, thereof andtheir subsequent processing, for example in order to detect the possiblepresence of visible defects on the surface, minimising the checking byhuman operators. The defects sought can for example be irregularities onthe surface of a tyre (unvulcanised compound, alterations in shape,etc.), structural unevenness, cuts, presence of foreign bodies on thesurface, etc.

The Applicant has observed that in order for the check to be able to beused “on line” inside a tyre production plant, it is necessary for thecheck itself to be carried out in short time periods and with low costs.

Therefore, the method for checking the tyre through acquisition andanalysis of images thereof to highlight possible defects thereofpreferably takes a time period that is kept within the aforementionedlimited “cycle time” period and at the same time ensures an accurateverification of the presence of defects in the tyre itself, atreasonably low cost.

The Applicant has observed that although the above documents in somecases effectively describe devices that can be useful for detectingspecific defects in a tyre, in order to detect a plurality of defects adifferent device would have to be used for each specific defect havingspecific characteristics for identifying the specific defect. TheApplicant has in fact further observed through an analysis of thedevices of the type illustrated in WO 2015/004587, EP 2322899 and US2011/018999 that a specific type of illumination coupled with a cameraor different sensor is preferred for the correct detection of a specificdefect or of a (limited) plurality of specific defects among the variousdefects that can occur in a tyre. The Applicant has indeed understoodthat the use of the same device with the same illumination and camerafor the analysis of the entire tyre would lead to the lack of detection,or very difficult detection, through image processing, of some defectsand in particular of some two-dimensional defects, i.e. that do notinvolve an alteration of the height of the surface, like for example thecuts at matching edges.

However, the provision of a large number of different devices each withdifferent characteristics to identify different defects increases thecomplexity of the tyre production line in the part dedicated to checkingthem and the costs thereof. Moreover, the provision of distinct devicesrequires continuous movement thereof towards the tyre when in analysisstep and away from it when a different device is in analysis step. Thisincreases the cycle time since the so-called “idle time” in which thetranslation of the unused devices takes place are substantial, even ifnecessary to avoid collisions or interference between distinct devices.

The Applicant has therefore set itself the problem of devising a methodand an apparatus for checking tyres capable of acquiring images of thesurface of a tyre, in particular for detecting more than one type ofdefect on the surface thereof, which are suitable for application online inside a tyre production line of a production plant, in other wordssuitable for being used to obtain reduced operating times and costs, andcapable of providing reliable results.

The Applicant has realised that having a detection system with at leasttwo light sources makes it possible to vary the illumination of aportion of the surface of the tyre according to the type of defectwished to be identified and to adapt the acquisition of images both indiffused light and in grazing light particularly useful for the purposesof the aforementioned check of the tyre according to whether or notfurther devices are used, such as a thrusting element for thedeformation of the tyre itself.

More precisely, the Applicant has finally found that a method and anapparatus providing for a first illumination step and a secondillumination step of a first surface portion and of a second surfaceportion of the tyre, respectively, surface portions that can generallyhave different defects, with consequent acquisition of a first image andof a second image, through the same device coupled, or not, with athrusting system, allows the checking of the tyre to be made fast.Advantageously, the first illumination step is carried out at the sametime as a deformation of the illuminated portion of the surface or atleast part thereof, using an illumination coming from a first lightsource, whereas the second illumination is carried out withoutcompression. This different illumination and acquisition of images iscarried out in the invention by the same detection system and by atleast two light sources.

In accordance with a first aspect, the invention concerns a method forchecking tyres.

Preferably, it is foreseen to provide a tyre to be checked.

Preferably, it is foreseen to associate a first light source and asecond light source able to be activated independently with a camera.

Preferably, it is foreseen to apply a first force against a firstsurface portion of said tyre so as to generate a deformed surfaceportion.

Preferably, it is foreseen to illuminate said deformed surface portionof said tyre with a first light radiation emitted by said first lightsource.

Preferably, it is foreseen to keep said second light source inactiveduring said deformation.

Preferably, it is foreseen to acquire a first image of said deformedsurface portion illuminated by said first light radiation through saidcamera.

Preferably, it is foreseen to remove said first force from said firstsurface portion of said tyre.

Preferably, it is foreseen to select a second surface portion at leastpartially distinct from said first surface portion of said tyre.

Preferably, it is foreseen to illuminate said second undeformed surfaceportion of said tyre with a second light radiation emitted by saidsecond light source.

Preferably, it is foreseen to acquire a second image of said secondundeformed surface portion illuminated by said second light radiationthrough said camera.

Preferably, it is foreseen to process said first image and said secondimage, so as to detect possible defects in said first surface portionand in said second surface portion of said tyre.

In accordance with a second aspect, the invention relates to anapparatus for checking a tyre.

Preferably, a support plane is provided configured to receive a tyre.

Preferably, a deformation element is provided configured to apply afirst force to a first surface portion of said tyre so as to generate afirst deformed surface portion.

Preferably, a positioning actuator is provided operatively associatedwith the deformation element and configured to move said deformationelement towards and away from said surface of said tyre.

Preferably, a device including a camera is provided.

Preferably, the device includes a first light source.

Preferably, the device includes a second light source.

Preferably, a processing unit is provided programmed to activate saidpositioning actuator so as to move said deformation element towards saidtyre to apply a force to a first surface portion of said tyre so as togenerate a first deformed surface portion.

Preferably a processing unit is provided programmed to activate saidpositioning actuator so as to remove said first force from said firstsurface portion of said tyre.

Preferably, the apparatus comprises a drive and control unit programmedto actuate said first light source so as to illuminate said firstdeformed surface portion of said tyre, keeping said second light sourceinactive during said deformation of said first surface portion.

Preferably, the drive and control unit is programmed to control saidcamera so as to acquire a first image of said first deformed surfaceportion illuminated by said first light source.

Preferably, the drive and control unit is programmed to actuate saidsecond light source so as to illuminate a second undeformed surfaceportion of said tyre at least partially distinct from said first surfaceportion.

Preferably, the drive and control unit is programmed to control saidcamera so as to acquire a second image of said second undeformed surfaceportion illuminated by said second light radiation.

Preferably, said processing unit is programmed to process said firstimage and said second image, so as to detect possible defects in saidfirst surface portion and in said second surface portion of said tyre.

The Applicant considers that providing a method and an apparatus inwhich a single device is capable of carrying out different types ofanalysis for detecting different types of defects makes the more generalmethod for checking a tyre faster and more reliable, with low costs. TheApplicant has indeed studied and provided a method and an apparatus inwhich it is possible to minimise the number of devices necessary tocarry out many distinct measurements using a first optimised source forthe illumination of defects visible through compression in a firstportion of tyre in combination with a second source for illuminating asecond portion of tyre in an optimised manner to detect another type ofdefect.

The present invention, in at least one of the aforementioned aspects,can also have one or more of the preferred characteristics describedhereinafter.

Preferably, said first light source is suitable for emitting diffusedlight radiation and said second light source is suitable for emittinggrazing light radiation.

Preferably, said second light source comprises a first sub-light sourceemitting a first sub-light radiation and a second sub-light sourceemitting a second sub-light radiation, in which for each point of saidsecond surface said first sub-light radiation and said second sub-lightradiation come, respectively, from two opposite half-spaces with respectto an optical plane of said camera.

Advantageously, this particular arrangement of the light sources makesit possible both to come particularly close to the tyre when thecompression thereof is carried out to detect a first type of defects inthe first surface portion, and to illuminate correctly and with thenecessary power to identify defects that could be present in the secondsurface portion.

More preferably, it is foreseen to arrange said first sub-light sourceand said second sub-light source symmetrically with respect to saidfirst light source.

A symmetry in the sources, in this case of the second source thatcomprises a first sub-source and a second sub-source, which are arrangedat the two sides of the optical plane of the detection system, allowseasier comparison of images detected by the camera while the secondsurface portion is illuminated with the first sub-light radiation orwith the second sub-light radiation. These illuminations are differentfor their different specular provenance.

Preferably, illuminating with a first light radiation comprisesilluminating said first surface portion or said second surface portionwith a first diffused light radiation.

Preferably, illuminating with a second light radiation comprisesilluminating said second surface portion with a first grazing sub-lightradiation or a second grazing sub-light radiation.

The first light source preferably emits a radiation on the first surfaceportion or on the second surface portion that, at the level of the firstsurface portion or second surface portion, is diffused, whereas thefirst sub-light source or second sub-light source emits a radiation onthe second surface portion that, at the level of the second surfaceportion is grazing. The first surface portion, deformed by thecompression, preferably only need diffused light to identify defects,whereas the second surface portion preferably needs an illumination withgrazing light and more preferably with two different types of radiation,grazing and diffused, so as to obtain the acquisition of at least twoimages for the same second surface portion, each with differentillumination, which can be compared with each other to identify thedefects on the second surface portion.

Preferably, for each point of said second surface portion at least 90%of the respective total light power of said first sub-light radiationand second sub-light radiation incident in the point comes,respectively, from said two opposite half-spaces defined by said opticalplane.

More preferably, for each point of said second surface portion theentire respective total light power of said first sub-light radiationand second sub-light radiation incident in the point comes,respectively, from said two opposite half-spaces. In this way, thecontrast between the two illuminations is accentuated.

Preferably, at least 75% of the respective total light power of saidsecond light radiation incident on each point of said second surfaceportion forms a first angle of incidence of size less than or equal to55° with a plane tangent to the surface of said tyre in said each point.

Preferably, at least 75%, more preferably at least 90%, of therespective total light power of said first sub-light radiation andsecond sub-light radiation incident on each point of said second surfaceportion forms a first angle of incidence of size less than or equal to55°, more preferably less than or equal to 50° with a plane tangent tothe surface of said tyre in said each point. In this way, the grazingeffect of the light is accentuated.

Preferably, at least 75%, more preferably at least 90%, of therespective total light power of said first sub-light radiation andsecond sub-light radiation incident on each point of said second surfaceportion forms a first angle of incidence of size greater than or equalto 10°, more preferably greater than or equal to 20°, even morepreferably greater than or equal to 30° with a plane tangent to thesurface of said tyre in said each point. In this way, the illuminationis possible also with light sources arranged in close proximity to thesurface of the tyre.

Preferably at least 75%, more preferably at least 90%, of the respectivetotal light power of said first sub-light radiation and second sub-lightradiation incident on each point of said second surface portion forms asecond angle of incidence less than or equal to 45°, more preferablyless than or equal to 30°, in absolute value, with a reference planeperpendicular to said optical plane in said each point and passingthrough the normal to the surface in said each point. In this way, thedifference in illumination between the first light radiation and thesecond light radiation is accentuated.

Preferably, providing a tyre includes arranging said tyre on a supportplane with axial mid-plane substantially parallel to the support plane,defining a resting side portion and a free side portion arranged at acertain height with respect to said support plane.

Preferably, applying a first force includes applying said first forceagainst a surface portion of said free side surface.

In order to obtain correct support of the tyre during inspection, it ispreferable for it to be rested on a plane so that a rotation axis of thetyre is substantially perpendicular to the support plane. In this way,the tyre is particularly stable and easy inspection of at least half ofsaid tyre is allowed.

Preferably, said first force includes a component in the direction of arotation axis of said tyre. The tyre is thus “compressed” along itsrotation axis so as to highlight defects, like for example cuts, whichmay be formed along a sidewall or a shoulder thereof.

More preferably, said component of said first force is in a directiontowards said mid-plane. Advantageously, the tyre is compressed from theoutside towards the inside, i.e. it is compressed by applying a force inan outer surface portion thereof facing towards the inside of the tyre.

Preferably, it is foreseen to bring said first light source towards saidfirst deformed surface portion at a distance comprised between about 25mm and about 55 mm, more preferably between about 35 mm and about 45 mm.The defects searched for can for example be irregularities on thesurface of a tyre (unvulcanised compound, alterations in shape, etc.),structural unevenness, presence of foreign bodies on the surface. Amongstructural unevenness defects, so-called “carcass creep” areparticularly critical, which are rare but potentially very dangerousdefects, generated in the interface region between two portions of thetyre having different chemical-physical characteristics, like forexample different compounds.

Such defects are in the form of small cuts, typically extendinglongitudinally, i.e. they follow the circular extension of the tyre,characterised by perfectly matching edges—between which there is noremoval or lack of material, this being a characteristic that makes themparticularly difficult to identify. The compound running can involveareas of the tyre arranged both inside and outside of the tyre itself,for example close to the inner surface, below the liner layer whereas onthe outside a non-adhesion of two adjacent compounds can generate cutstypically in the buttress or sidewall area.

By suitably deforming a first portion of side wall of a tyre to bechecked it is possible to decrease the outer radius of curvature of adeformed surface portion of the tyre, thus highlighting possibledefects, in particular compound running and other cuts or holes, sincethe accentuation of the normal external convexity tends to ‘open’ theedges or perimeters of such defects, making them easier to identify inthe subsequent image processing.

The images detected of this adequately compressed first surface portionthus have a high quality and/or contain information in number andquality such as to allow a subsequent automatic processing of the latterin order to detect possible defects existing, making the algorithms forautomatically detecting defects used for this purpose highly effective.

This type of defect, in order to be properly identified, requires anillumination of relative high power and close to the deformed portion oftyre, i.e. positioning of the device very close to the thrustingelement, otherwise the cut opened by the thrusting element “closes” assoon as a distance is reached from the area in which the deformationtakes place.

Preferably, it is foreseen to bring said first light source towards saidsecond surface portion at a distance comprised between about 25 mm andabout 55 mm, more preferably between about 35 mm and about 45 mm. Thisrange of distances has been found to be optimal for correctvisualisation of the defects: the distance at which the first lightsource is positioned is an optimal compromise between the minimumdistance so as not to hit the tyre or an element that applies acompression force on it.

Preferably, it is foreseen to apply a second force against a thirdsurface portion of said tyre so as to generate a second deformed surfaceportion, said third surface portion being at least partially distinctfrom said first surface portion and from said second surface portion ofsaid tyre.

Preferably, it is foreseen to illuminate said second deformed surfaceportion of said tyre with said first light radiation emitted by saidfirst light source.

Even more preferably, it is foreseen to acquire a third image of saidfurther deformed surface portion illuminated by said first lightradiation through a detection system. Advantageously, more than onesurface portion of tyre is checked through the device by applying aforce in different portions of the tyre. In this way, defects in variouspositions of the surface can be detected.

Preferably, said first surface portion or said third surface portionbelongs to said free side surface. The tyre is advantageously examinedin the free side surface, i.e. the surface not in contact with asupport. Preferably, in order to examine the side surface in contactwith the tyre substantially symmetrical to the free side surface, thetyre is rotated by 180° perpendicularly to its rotation axis so that theside surface previously in contact with the support becomes the freeside surface and can be examined.

Preferably, illuminating said second surface portion includesilluminating said second surface portion with said first lightradiation.

Preferably, illuminating said second surface portion includesilluminating said second surface portion with said second lightradiation at a different time with respect to the time at which saidfirst light radiation illuminates said second surface portion.

The type of defects searched for in the second surface portion of thetyre is identified preferably by comparing images acquired through thedetection system in different illumination conditions, like the firstlight radiation and the second light radiation, so that the defect isdetectable for example through a “subtraction” of the characteristicsdetectable in one image from the other.

Preferably, illuminating said third surface portion with a first lightradiation comprises illuminating said third surface portion with a firstdiffused light radiation. Advantageously, the type of illumination ofthe third portion is substantially analogous to the type of illuminationof the first surface portion.

Preferably, illuminating said second surface portion includesilluminating said second surface portion with said first lightradiation.

Preferably, illuminating said second surface portion includesilluminating said second surface portion with said first sub-lightradiation at a different time with respect to the time at which saidfirst light radiation illuminates said second surface portion;

Even more preferably, illuminating said second surface portion includesilluminating said second surface portion with said second sub-lightradiation at a different time with respect to the time at which saidfirst light radiation illuminates said second surface portion and saidfirst sub-light radiation illuminates said second surface portion.

The three distinct images acquired to be processed are each with adifferent type of illumination. This allows a comparison of threedistinct images and their processing with suitable algorithms in orderto highlight the possible defects in the second surface portion.

More preferably, acquiring said second image includes acquiring a firstimage to be processed when said second portion is illuminated by saidfirst light radiation.

Even more preferably, acquiring said second image includes acquiring asecond image to be processed when said second portion is illuminated bysaid first sub-light radiation.

Even more preferably, acquiring said second image includes acquiring athird image to be processed when said second portion is illuminated bysaid second sub-light radiation.

The three images to be processed, two preferably in grazing light andone in diffused light, are thus advantageously processed to identifydefects.

Even more preferably, said first image to be processed, second image tobe processed or third image to be processed are made up of a respectiveplurality of first linear images, second linear images or third linearimages of a succession of linear surface portions, contiguous to oneanother or partially overlapping, said first linear images, secondlinear images or third linear images being acquired on each linearportion of said succession of linear portions illuminated, respectively,by said first light radiation, first sub-light radiation and secondsub-light radiation in alternate sequence.

Advantageously, said first image, said second image, said third image orsaid images to be processed are digital images. More preferably they areimages formed from pixel matrices.

Preferably, said first image or said third image is made up of arespective plurality of fourth linear images of a succession of linearsurface portions, contiguous to one another or partially overlapping,said fourth linear images being acquired on each linear portion of saidsuccession of linear portions illuminated, respectively, by said firstlight radiation.

A type of detection system for acquiring images is for example a linearcamera defining a lens line, intersection of the lens plane on a focalplane in which or close to which the first surface portion or the secondsurface portion or the third surface portion is preferably arranged whenilluminated. The linear portions are therefore preferably surfaceportions able to be obtained close to said lens line in temporalsuccession. For example, such a succession of linear portions can beobtained by rotating the tyre about a rotation axis thereof, or byrotating the detection system and the light sources about the tyre.Preferably, at least one complete rotation of 360° is completed. Morepreferably, a rotation of more than 360° is carried out to have correctoverlapping between the initial and end part (which must match) of thetyre where the images start and finish being taken, respectively.

Preferably, it is foreseen to rotate said tyre about its rotation axis;and to illuminate said tyre in a plurality of angular positions of saidtyre so as to obtain a plurality of first images or of second images orof third images at different angular positions, a first image, or asecond image, or a third image for each angular position of said tyre.

Advantageously, the tyre is rotated, instead of the detection system,since the first operation is simpler: the rotation of the detectionsystem could lead to it being damaged or inaccurate acquisition of theimages due to vibrations induced by the continuous movement.

Preferably, said first surface portion or said third surface portion isan outer surface portion of a sidewall or of a shoulder of said tyre.

Preferably, said second surface portion is a surface portion of a beadof said tyre.

Preferably, the first type of defects mentioned, in which preferably astrong illumination and a compression of the surface portion underexamination are necessary, is a defect that can be found at the sidewallor shoulder of the tyre. The second type of defect, requiring aplurality of different illuminations, is most frequent at the level ofthe bead of the tyre.

Preferably, applying a first force or a second force includes applying aconstant pressure to said first deformed surface or to said seconddeformed surface of said tyre during said rotation.

Even more preferably, a value of said constant pressure depends on atype of said tyre to be checked.

Preferably, applying a first force or a second force against a firstsurface portion of said tyre or against a third surface portion of saidtyre so as to generate a first deformed surface portion or a seconddeformed surface portion includes keeping said first deformed portion orsecond deformed portion at a predetermined height with respect to asupport of said tyre.

A deformation can be applied either at constant force or at constantheight. Both can be used and the most advantageous is selected accordingto the specific application or the type of tyre to be checked.

More preferably, said height depends on the model of tyre to be checked.

In fact, not all tyres are the same size or have the same rigidity andtherefore the height at which to position the deformed surface of thetyre is preferably selected based on the characteristics of the tyreitself.

Preferably, it is foreseen, before illuminating said second surfaceportion, to move said second light source from a first inactiveconfiguration where it is controlled not to emit light radiation and inwhich the distance of said second source from a focal plane of saidcamera is greater than the distance of said first source from said focalplane to an active configuration in which it is adapted to emit a secondlight radiation and in which the distance of said second source fromsaid focal plane is equal to or less than the distance of said firstsource from said focal plane.

In this way, two illuminations can be obtained by moving the firstsub-light source and the second sub-light source according to whetherone or both are necessary. When in inactive configuration, the device isparticularly compact and adapted for going substantially close to thefirst or third surface portion of the tyre, which is deformed. In thesecond configuration, with the first sub-source and the secondsub-source “open”, it is possible to obtain a plurality of differentilluminations of the second surface portion through the differentsources. In the second configuration, in fact, the compactness is lessnecessary since neither the compression means nor the consequentdeformed surface are present, both no longer necessary for detecting thedefect sought, for example a cut in the bead area.

Preferably, a robotic arm is provided coupled with one end to saiddevice. Through a robotic arm, the device for the illumination ofsurface portions of the tyre is easily moved so as to reach the positionof the portion to be examined.

Preferably, the processing unit is programmed to move said robotic armtowards said first deformed surface so that said first light source ofsaid device is brought to a distance comprised between about 25 mm andabout 55 mm from said deformed surface, more preferably between about 35mm and about 45 mm.

Preferably, said deformation element includes a thrusting roller.

More preferably, the thrusting roller is mounted so as to be able torotate freely about its own axis. Advantageously, the compression takesplace through the roller resting against a surface portion of tyre. Theroller, being able to rotate, keeps the portion compressed for arotation of the tyre about its rotation axis, so that the same surfacecan be checked in any angular position.

Preferably, the tyre is set in rotation and the position of the rollerremains the same, rotating about its axis due to the rotation of thesurface of the tyre with which it is in contact.

More preferably, the axis of the thrusting roller lies on a planepassing through a rotation axis of the tyre and through the radialdirection of the deformed surface portion. In this way, an optimalcompression of the surface of the tyre is carried out.

Preferably, said rotation axis of said thrusting roller can bepositioned at a predetermined angle with a rotation axis of said tyre.In this way, it is possible to “follow” the geometric shape of thesurface of the tyre in an optimal manner, suitably inclining therotation axis of the roller, so as to apply a correct pressure that isnot modified by the geometric shape of the tyre.

Preferably, the thrusting roller can be positioned in two distinctpositions. In the first, the rotation axis of the roller issubstantially perpendicular to the rotation axis of the tyre. In thesecond, the rotation axis of the roller and the rotation axis of thetyre form an angle of about 120°.

Preferably, said roller includes a portion with increased section at acentral portion along said rotation axis and a portion with reducedsection at an end thereof along said rotation axis. The central portionwith increased section is preferably positioned at the shoulder orsidewall area where it is wished to look for defects. However, a largecentral portion can in certain situations create vibrations passing overthe blocks of the tyre. For this reason, a tapering of the axial ends ofthe roller itself is preferable, so that the area of the surface engagedby the compression of the roller is limited and adjustable.

Further characteristics and advantages will become clearer from thedetailed description of some example, but not exclusive, embodiments ofa method and a device for checking tyres, in accordance with the presentinvention. Such a description will be outlined hereinafter withreference to the attached figures, provided only for indicating andtherefore not limiting purposes, in which:

FIG. 1 shows a partial and schematic perspective view, partially insection and partially in terms of functional blocks, of an apparatus forchecking tyres in a tyre production line;

FIG. 2 shows a partial and schematic perspective view of the apparatusfor checking tyres in accordance with the present invention of FIG. 1 inan operative step;

FIG. 3 shows the apparatus of FIG. 2 in a distinct operative step;

FIG. 3a shows a detail of the apparatus of FIG. 3 in enlarged scale;

FIG. 4 shows the apparatus of FIGS. 2-3 in a further operative step;

FIG. 4a shows a view from above of the apparatus in the operativeconfiguration of FIG. 4;

FIG. 5 shows a partial and schematic side view of a detail of theapparatus of FIG. 2 or 3;

FIG. 6 shows a partial and schematic side view of a detail of theapparatus of FIG. 4;

FIG. 7 shows a schematic section side view of a detail of FIG. 5 or 6;

FIG. 8 shows a partial and schematic perspective view of a detail of theapparatus of FIG. 2 or 3;

FIG. 9a shows a perspective view of a device for checking tyres in anoperative configuration in accordance with the present invention;

FIG. 9b shows a perspective view of the device for checking tyres ofFIG. 9a in a different operative configuration;

FIG. 10 shows a view from above of the device of FIG. 9 a;

FIG. 11 shows a front view of the device of FIG. 9 a;

FIG. 12 shows a view from above of the device of FIG. 9b ; and

FIG. 13 shows a front view of the device of FIG. 9 b.

An apparatus for checking tyres in a tyre production line according tothe present invention is globally indicated with 1 and depicted inFIG. 1. In general, the same reference numeral will be used for possiblevariant embodiments of similar elements.

The apparatus 1 comprises a support 102 (only visible in FIG. 1) adaptedfor supporting a tyre 200 on a sidewall and for rotating it about itsrotation axis 201, typically arranged according to the vertical. Thesupport 102 is typically actuated by a moving member not described andillustrated any further, since it can as an example be of the knowntype. The support for the tyre can possibly be configured to lock it,for example the respective resting bead. The tyre 200 rested in thesupport therefore defines a free side surface or free sidewall,representing that surface portion not resting on the support and facing,in a system of coordinate axes with an axis Z perpendicular to the planeof the support, upwards.

The tyre 200 has a substantially toroidal structure about the rotationaxis 201, and has an axial mid-plane 242 (represented in section by abroken line in FIGS. 2, 3 and 4) perpendicular to the rotation axis 201.The tyre is made up of a crown 203 and side walls 204. In turn, thelatter are each made up of a shoulder area 205, a bead area 206 and aradially central or sidewall area 207 interposed between shoulder andbead. Typically, as represented now in FIGS. 2 and 3, the apparatus 1comprises a robotic arm 220 on which a device 10 is mounted, and inparticular the device 10 comprises an attachment member 19 for couplingwith an end of the robotic arm 220. The robotic arm 220 represented in avery schematic manner in FIG. 2, is preferably an anthropomorphicrobotic arm. Even more preferably, it is an anthropomorphic robotic armwith at least 5 axes.

Preferably, the apparatus 1 also includes a deformation element 130. Thedeformation element 130 is configured to apply, through physicalcontact, a compression force on an outer contact surface belonging to aportion of a side wall of the tyre 200 in order to elastically deform aportion of side wall, preferably of the free side surface. In apreferred configuration, shown as an example in FIGS. 2 and 3, thecompression force (indicated by the vertical arrow F in FIGS. 2 and 3)is directed like a rotation axis 201 of the tyre 200. However, accordingto the Applicant the present invention includes the cases in which thecompression force has at least one component parallel to the rotationaxis 201.

Preferably, the deformation element 130 comprises a compression member131 and a positioning actuator 132 adapted for moving the compressionmember along the direction of the compression force. As an example, thepositioning actuator 132 can be a pneumatic cylinder. Therefore, thecompression member can be brought into contact with or away from thetyre 200. Preferably, the compression member 131 comprises a thrustingroller.

Preferably, the thrusting roller is rotatable about its rotation axis,indicated with 117 in the figures. The axis 117 of the thrusting rolleralways sits on a plane passing through the axis of the tyre and throughthe radial direction of the portion of side wall subjected todeformation (for example the plane of FIGS. 2 and 3). Preferably, theaxis 117 of the thrusting roller, in the absence of forces, in otherwords in rest position, is perpendicular to the axis of the tyre. Theaxis of the roller, in operation, can diverge from such a perpendicularcondition with the axis of the tyre (as shown for example in FIG. 2) forexample within the range +30° from the perpendicular condition.

Furthermore, the thrusting roller, visible in detail in FIG. 3a ,comprises a section, taken in a plane perpendicular to the rotation axis117, that is substantially circular. A diameter of the section ispreferably variable, from a minimum diameter present at a first end 118a and a second axially opposite end 118 b of said roller along therotation axis 117, to a maximum diameter present in a central area ofthe roller.

Preferably, the deformation element 130 comprises a radial movementmember (not shown, for example a further electric motor and a system ofguides and sliding blocks to guide the radial movement) adapted formoving the compression member 131 and the positioning actuator 132 as aunit along the radial direction of the tyre. Therefore, the deformationelement 130 can be taken away from the tyre when not in use.

Preferably, the deformation element 130 is adapted for elasticallydeforming a portion of a side wall of the tyre 200, applying acompression force on an outer contact surface belonging to the portionof side wall, pressing the aforementioned thrusting roller on the outercontact surface. The force applied or the movement imposed on the outercontact surface along a rotation axis of the tyre is predetermined anddepends on the type of tyre to be checked. The tyres 200 can have adifferent elasticity and deformability according to the type and model,and therefore the force applied or the deformation imposed by thedeformation element 130 is preferably dependent on the type of tyre 200to be checked.

The device 10, with initial reference to FIGS. 5-8, comprises adetection system 104 including a camera 105. Preferably, the camera 105is a linear camera having a lens line 106 lying on an optical plane 107passing through the camera itself (visible in FIGS. 5, 6 and 8). Thepresent invention also considers the alternative case in which thecamera 105 is of a different type, like for example a matrix camera. Inthis case, the surface portion illuminated and acquired is also of thematrix type. Moreover, the camera 105 defines a focal plane 121 in whicha portion to be illuminated of tyre surface is focused upon. Preferably,the optical plane 107 and the focal plane 121 are perpendicular to eachother (visible in FIGS. 5, 6 and 8).

The device 10 also comprises a first light source 110 and a second lightsource 108 adapted for emitting, respectively, a first and a secondlight radiation to illuminate a surface portion 202, preferably linear(visible in FIG. 8), of said tyre 200 coinciding with the lens line 106(for example when the surface portion is planar) or close to the lensline 106 (due to the curvilinear shape of the surface of the tyre).

The detection system through the camera 105 is adapted for acquiring arespective two-dimensional digital image of the surface portion 202(linear) illuminated by at least one from the first and the second lightradiation.

Preferably, the second light source 108 comprises a first sub-lightsource 109 a and a second sub-light source 109 b. Each sub-light source109 a and 109 b can comprise one or more source elements. Preferably,each sub-light source 109 a and 109 b comprises a single respectivesource element 111 and 112, respectively. The two source elements 111,112 are positioned symmetrically with respect to the optical plane 107.Preferably, the two source elements 111 and 112 respectively sit onopposite sides with respect to the optical plane and are equidistantfrom it.

Preferably, the first light source 110 comprises two respective sourceelements 113 distributed on both sides of the optical plane 107 andsymmetrically with respect to such a plane.

Each source element 111, 112, 113 has a respective main direction ofextension (indicated as an example with the broken lines 114 in FIG. 8)preferably substantially parallel to the optical plane 107 and thus tothe lens line 106.

As an example, the source elements 111, 112, 113 have a dimension alongthe main direction of extension 114 equal to about 60 mm, and a diameterperpendicular to the aforementioned main direction of extension 114equal to about 25 mm. Each source element 111, 112, 113, typicallycomprises a plurality of LED sources 169 arranged aligned along the maindirection of extension 114. Preferably, as can be seen in FIG. 7, eachsource element 111, 112, 113, comprises, positioned above each LED light169, a converging lens 170, adapted for converging the light beamemitted by the LED light by about 30°. The beam of light emitted by eachLED light is therefore preferably restricted within an angle comprisedbetween about 20° and about 40°.

In FIGS. 5, 6 and 8, the elements of the light sources 111, 112, 113 areshown schematically with reference to their respective emitting surface(in the figures as an example semi-circular in shape, however it can beof any shape), which can for example coincide with the transparentprotective glass and/or diffusor.

As can be seen from FIGS. 5 and 6, the device, and in particular itslight sources, can be moved from a first operative configuration to asecond operative configuration and vice-versa.

In the first operative configuration of FIG. 5, preferably the distanced₁ of each of the source elements 113 of the first light source 110 fromthe optical plane 107 is greater than the distance d₂, d₃ between eachsource element 111, 112 of said second light source 108 and the opticalplane 107.

Advantageously, in the second configuration of FIG. 6, the distance d₁between the first source 110 at the source elements 113 and the focalplane 121 is less than the distance d₂ or d₃ of the first sub-lightsource 109 a or second sub-light source 109 b from the focal plane 121.More preferably d₁ is less than both d₂ and d₃. Even more preferablyd₂=d₃. Preferably, in both configurations, the two source elements 113of the first light source 110 are coplanar and define a plane P1substantially parallel to the focal plane 121, being a distance d₁ fromit, i.e. the source elements 113 of the first light source are the samedistance from the focal plane 121. The plane P1 can be defined as theplane passing through the points of both source elements 113 of thefirst light source 110 at minimum distance from the focal plane 121 (asrepresented in FIGS. 5 and 6), or as the plane passing through a middleline of both source elements 113.

Preferably, the sub-light sources 109 a and 109 b, preferably both inthe first and in the second operative configuration, are also coplanarand define a plane P2 substantially parallel to the focal plane 121.Preferably, the distance of this plane P2 from the focal plane 121 isequal to d₂ (con d₂=d₃). Like for P1, the plane P2 can be defined as theplane passing through the points of both sub-light sources 109 a and 109b at minimum distance from the focal plane 121 (as represented in FIGS.5 and 6), or the plane passing through a middle line of both sub-lightsources 109 a-109 b.

Preferably, in the first and/or in the second configuration, thedistance d₁ is equal to about 77 mm.

More preferably, in the first configuration, the distance d₁−d₂=d₁−d₃ isequal to about 32 mm (77 mm−45 mm).

An embodiment of this device is represented in FIGS. 9a, 9b , and 10 to13.

Each light source 108, 110 includes a support, preferably made ofaluminium, on which the LEDs 169 are fixed. The supports are allindicated with 168 in the attached figures (see FIGS. 9a, 9b and 13).Preferably, the LEDs 169 are fixed to the respective support 168 througha thermo-conductive paste (not visible in the figures). Advantageously,each support 168 also includes, in an outer surface not in contact withthe LEDs, a fin arrangement 167 for the dissipation of heat (visible inFIGS. 9a and 13).

The first and the second source element 113 of the first light source110 are positioned between two plates 11, 12 arranged substantiallyperpendicular to the main direction of extension 114 of the first lightsource 110 and substantially parallel to one another. Between the twoplates 11, 12, which extend downstream of the first light source in thedirection of emission of the light, the linear camera 105 is alsopositioned.

These two plates 11, 12 are hinged to a third and a fourth plate 13, 14,so that the rotation axis of the third and fourth plate thus defined issubstantially parallel to the main direction of the first light source110 or of the second light source 108. The third plate 13 is firmlyconnected to the first sub-source 109 a of the second light source 108,whereas the fourth plate 14 is firmly connected to the second sub-lightsource 109 b of the second light source 108.

Third and fourth plate 13, 14 are rotationally moved by a first and asecond pneumatic piston 15, 16, visible in extended condition in FIGS.9a and 10. Each piston 15, 16 is connected at one end to the plate to bemoved, and at the other end to the first plate 11.

The movement of the plates 13, 14 through the pistons means that thedevice 10 can be brought into the first operative configuration such asthat of FIGS. 9a , 10 and 11 in which the second light source 108, i.e.the sub-sources 109 a and 109 b, are brought “forwards”, i.e. they arefurther from the camera 105 with respect to the first light source 110and closer to the tyre surface to be illuminated, i.e. closer to thefocal plane 121 with respect to the first light source 110; or in thesecond configuration, such as that represented in FIG. 9b , in which thesecond light source 108 is positioned further away with respect to thefocal plane 121, the first sub-source 109 a and the second sub-source109 b are substantially bent parallel to the optical plane 107 tominimise a bulk given by the device 10 in a direction perpendicular tothe optical plane 107.

Preferably, both in the first operative configuration and in the secondoperative configuration, as can be seen more clearly from the respectiveFIGS. 11 and 13, the source elements of the first light source 110 andof the second light source 108 are arranged so that for their entireextension in a view perpendicular to the optical plane 107 they laybetween two planes perpendicular to the lens line. In other words, allof the first and second ends of the sources 108 and 110 with respect tothe main direction of extension 114 lay on a respective planeperpendicular to the lens line.

Preferably, the device 10 comprises a drive and control unit 140configured to selectively activate one or more of said first lightsource 110, and said second light source 108 and activate the linearcamera 105 to acquire a respective two-dimensional digital image (incolour or monochromatic) of the linear surface portion, preferably insynchrony with the activation of one or more of said first light source110 and second light source 108.

Preferably, the drive and control unit 140 is fixed to said supportplate 11 of the first light source 110 and of the camera 105 so as tosend signals relative to the control of the light sources 108, 110,without waiting times. Preferably, moreover, the drive and control unit140 is adapted for controlling the second light source 108 to not emitany radiation when in the second configuration and to emit lightradiation when in the first configuration.

For greater heat dissipation, moreover, the unit 140 also comprises afin arrangement 166 (visible in FIG. 9a ).

The processing unit 180, on the other hand, (illustrated in FIG. 1) ispreferably adapted for controlling the pistons 15, 16 so as to move thesub-light sources 109 a and 109 b of the second light source 108.Preferably, the processing unit 180 is also adapted for controlling thedeformation element 130 and the robotic arm 220 so as to bring thedeformation element 130 towards or away from the tyre 200 to deform, ornot, a surface portion, while the robotic arm 220 carries the device 10to a predetermined distance from the surface of the tyre to beilluminated and to be checked.

Preferably, the second light source 108 is suitable for illuminating thelens line 106 with grazing light. Preferably, the first light source 110is adapted for illuminating the lens line 106 with diffused light.

Preferably, the apparatus 1 is made to operate according to the methodof the invention.

A first surface portion to be checked (always indicated with 202) isselected in the outer surface of the tyre 200. Preferably, but notexclusively, this portion belongs to the shoulder or to the sidewall ofthe tyre 200. The processing unit 180 takes the device 10 into thesecond configuration of FIGS. 9b , 12, 13 and 6, whereas the drive andcontrol unit 140 controls the second light source 108 to not emit anyradiation. The device 10 is particularly compact for the positioning ofthe sub-light sources 109 a and 109 b substantially parallel to theoptical plane 107.

The processing unit 180 controls the deformation element 130 to makecontact with the tyre, preferably at its side wall 204, so as to apply aforce against it and deform a first surface portion thereof includingthe selected first portion, as can be seen in FIG. 2. Preferably, asrepresented in FIG. 2, the first surface portion is a portion of theshoulder 205 of the tyre 200. Preferably, the entire remaining portionof the side wall 204 of the tyre 200 remains undeformed. As an example,the compression force is such as to deform the portion of side wall 204so that the maximum excursion, taken between all of the points of saidportion of side wall, between the position in the absence of forces andthe deformed position, the excursion being measured along the directionof the compression force, is equal to a value comprised between about 10and about 20 mm.

The device 10 in the compact configuration of FIG. 9b can comesubstantially close to the deformation element 130 (again see FIG. 2) toilluminate and acquire images of the first surface portion of tyre 200deformed by the deformation element 130. The processing unit 180controls the robotic arm 220 to bring the first light source 110 towardsthe surface of the tyre 200 and the deformation element 130, so that alinear surface portion inside the first deformed portion at leastpartially coincides with or is close to the lens line 106 in the focalplane 121. The linear portion also belongs, at least partially, to thefirst deformed surface portion on the side of the deformation element130. Preferably, the distance between deformation element 130, and inparticular the thrusting roller and the device 10 is comprised betweenabout 30 mm and about 50 mm.

The processing unit 180, therefore, controls the movement member of thesupport 102 to set the tyre 200 in rotation.

As a function of the angular position signal received by the encoder,with the rotation of the tyre in progress, the drive and control unit140 cyclically activates in rapid sequence the first light source 110and the linear camera 105 to acquire a respective two-dimensionaldigital image (in colour or monochromatic) of the respective linearsurface portion in synchrony with the activation of the first lightsource 110. The control unit 140 will control in parallel the switchingon of the source elements 113 of the first light source 110 that work insynchrony with the linear camera 105. The two source elements 113therefore switch on at the same time.

More preferably, the drive and control unit 140 controls the first lightsource 110 to emit a diffused radiation on the first surface portion 202of the tyre 200, for example at a predetermined frequency. Such astroboscopic frequency is for example equal to 0.1 ms. The drive andcontrol unit 140, furthermore, controls the camera 105 to acquire animage of the first surface portion illuminated by the first light sourcein synchrony with the illumination thereof. Therefore, an image of thefirst surface portion of tyre 200 illuminated is acquired by the camera105 each time the first light source 110 that illuminates the portionwith diffused light is switched on.

Once the desired rotation of the tyre 200 has been carried out toexamine the desired surface portion, preferably at least one completerotation to acquire the entire circular extension, a digital image of atyre “ring” is obtained, made with all of the digital images of thesequence of linear portions each illuminated with the first lightsource. For a complete 360° image for example 25,000 single linearimages are used.

Optionally, a third portion of the surface of the tyre is selected,preferably but not necessarily again belonging to the sidewall 204 ofthe outer surface thereof, but distinct—at least partially—from thefirst portion. The deformation element 130 can thus be positioned,preferably again through the processing unit of the apparatus 180, at adistinct surface portion of the tyre 200, so as to deform a secondsurface portion of the tyre, including the selected third portion. Inthis way, a new analysis can be carried out, bringing the device 10towards the new position so as to obtain an illumination of the furtherdeformed outer surface portion of the tyre. See for example thedifference between the position of the deformation element 130 in FIG. 2and in FIG. 3 and the consequent different position of the device 10 inthe two figures: in FIG. 2 an outer surface portion of shoulder 205 ofthe tyre is illuminated by the first light source 110, whereas in FIG. 3an outer surface portion of the central area 207 of the sidewall 204 ofthe tyre 200 is illuminated by the first light source 110. Moreover, inFIG. 2, the rotation axis 117 of the thrusting roller, positioned at theshoulder 205, is inclined with respect to the plane defined by thesupport of the tyre 200, whereas in FIG. 3 the rotation axis 117 of thethrusting roller is substantially perpendicular to the rotation axis201, thus parallel to the aforementioned plane defined by the support102 of the tyre 200.

Furthermore, a second portion of the outer surface of the tyre 200 to bechecked is selected. Preferably, but not necessarily, this secondportion belongs to the bead 206 of the tyre 200.

The processing unit 180 controls the deformation element 130 to moveaway from the surface of the tyre so that no deformation force isapplied on it. Moreover, the unit 180 controls the pistons 15, 16 so asto take the second light source 108 into the operative configuration ofFIGS. 9a , 10, 11 and 5. Furthermore, the processing unit 180 controlsthe robotic arm 220 to take the device 10 towards the second surfaceportion, part of the bead of the tyre, and controls the movement memberof the support 102 to set the tyre 200 in rotation. The configurationreached is represented in FIGS. 4 and 4 a.

The first light source 110 and the second light source 108 are alsocontrolled by the drive and control unit 140 to emit a radiation on thesecond surface portion 202 of the tyre 200. Preferably, the first lightsource 110 emits diffused radiation on the second surface portion,whereas the second light source 108 emits grazing radiation, coming fromopposite half-spaces with respect to the optical plane 107 thanks to theprovision of the two sub-sources 109 a and 109 b. Preferably, all of thelight sources emit light radiation to illuminate the second surfaceportion of tyre, for example at a predetermined frequency. Such astroboscopic frequency is for example equal to 0.064 ms. Preferably, thelight sources, i.e. the first light source 110, the first sub-lightsource 109 a and the second sub-light source 109 b, are switched onalternately, i.e. in a given time period only the first source 110 orthe first sub-source 109 a or the second sub-light source 109 b of thesecond source 108 illuminates the second surface portion of tyre. Thedrive and control unit 140, furthermore, preferably controls the camera105 so as to acquire an image of the second surface portion illuminatedby the first source or by the first sub-source or by the secondsub-light source in synchrony with the illumination thereof. Therefore,advantageously, the camera 105 acquires an image of the second surfaceportion of tyre 200 illuminated each time the first light source 110 isswitched on, which illuminates the portion with diffused light, an imageof the second surface portion of tyre 200 illuminated every time thefirst sub-light source 109 a is switched on, which illuminates thesecond portion with grazing light from one side of the optical plane 107and an image of the second surface portion of tyre 200 illuminated everytime the second sub-light source 109 b is switched on, which illuminatesthe second portion with grazing light from the other side of the opticalplane 107. In this way, advantageously, for every second surface portionthree distinct images to be processed are acquired in which the sameportion is illuminated with a radiation having distinct characteristics.In this way, it is possible to acquire both an image in diffused lightand two images in grazing light of the same surface portion. These threeimages can also form distinct portions of a single two-dimensionalimage, in which a first portion is obtained with the grazing light, asecond portion with grazing light from a first direction of the opticalplane (for example from the right) and a third portion with grazinglight from a second opposite direction of the optical plane (for examplefrom the left).

Preferably, each image is a linear image.

Preferably, the apparatus comprises an encoder (not shown) to detect theangular position of the support, the drive and control unit beingconfigured to activate said first light source 110, and second lightsource 108, and to control the detection system as a function of anangular position signal of the support sent by the encoder.

As an example, the time difference between the acquisition of the firstand second linear image, as well as between the second and third linearimage and then cyclically between the first and third linear image, isless than 0.2 milliseconds.

Therefore, for substantially the same surface portion three linearimages are obtained, each with a different illumination.

The expression “substantially said surface portion”, or, later on,“substantially a same surface portion”, mean that the first and secondor third light source illuminate two (or three) respective surfaceportions hat can be spatially shifted from one another but arecomparable according to the present invention, i.e. show the sameelements substantially in the same position. For example the two (orthree) surfaces can be shifted, on the plane of the surface itself, by adistance of less than 0.2 mm, preferably less than, or equal to, 0.1 mm.Advantageously, said distance is less than, or equal to, the lineardimension of surface associated with a pixel (the latter as an examplebeing equal to 0.1 mm), in the case in which the detection systemincludes a camera, for example matrix or linear. In other words, eachpixel of the first image shows a micro-surface portion that is less than0.2 mm away from the micro-surface portion shown by the pixel of thesecond image corresponding to each said pixel.

In other words, the three images can be substantially overlapped pixelby pixel, although the real linear surface portion associated with asingle linear image does not coincide exactly for the three images, dueto the rotation of the tyre that has occurred in the meantime. However,the choice of the acquisition frequency of the images and of therotation speed is such that the three images are interlaced and thuscomparable pixel by pixel. Advantageously, each pixel of the first (orsecond or third) image shows a micro-surface portion that differs fromthe micro-surface portion shown by the pixel of the second (orrespectively third or first) image corresponding to each said pixelapart from the linear surface dimension associated with a pixel, as anexample the spatial shift being equal to about one third of a pixel. Inthis way, the three images are interlaced and the acquisition of thethree linear images takes place in a time period during which the tyrehas rotated by a portion equal to a pixel (as an example equal to about0.1 mm).

Once the desired rotation of the tyre has been carried out to examinethe desired surface portion, preferably at least one complete rotationto acquire the entire circular extension, a single digital image isobtained that is made with all of the digital images of the sequence oflinear portions each illuminated with a respective light source. Theprocessing unit 180 receives such an image from the detection system 104and extracts the corresponding first, second and third image of theentire desired surface portion therefrom.

In the case in which a single image is acquired as described aboveformed from a portion with diffused light [A], a portion with grazinglight dx [B] and a portion with left grazing [C], a succession repeateduntil the entire tyre is acquired, an overall image is obtained formedby the sequence ABCABCABCABCABCABCABCABCABC . . . . In processing thisimage is divided into three effective images, obtaining AAAAAAAA . . .BBBBBBBB . . . CCCCCCCC . . . .

Preferably, the processing unit 180 is also configured for the followingfunctions: receiving the images acquired from the linear camera 105; andprocessing the images in order to check the surface portion. Theprocessing unit 180 comprises for example a PC or a server. Preferably,the processing unit 180 is adapted for processing the second and thirdimage to be processed obtained with grazing light by comparing them inorder to obtain information on an altimetric profile of the surfaceportion. Preferably, the comparison between the second and third imageto be processed comprises calculating a difference image in which eachpixel is associated with a value representative of the differencebetween the values associated with the corresponding pixels in thesecond and third image to be processed.

Preferably, before comparing the second and third image to be processedit is foreseen to equalise the second and third image to be processed,for example equalising the average luminosity thereof globally orlocally.

Preferably, the processing unit 180 processes the first image to beprocessed in diffused light to detect the possible presence of defectson the surface portion, using the information obtained by theaforementioned comparison between the second and third image to beprocessed.

Preferably, the processing unit 180 is configured to calculate thedifference between the second and the third image in order to obtaininformation on an altimetric profile (e.g. possible presence or absenceof projections and/or depressions) of the linear surface portion.

Preferably, calculating the difference between the second and thirdimage comprises calculating a difference image in which each pixel isassociated with a value representative of the difference between thevalues associated with the corresponding pixels in the second and thirdimage. In this way it is possible to use the image obtained from thedifference between the second and third image to highlight thethree-dimensional elements (such as the raised pitting on the innersurface of the tyre or the raised writing) and take into account suchinformation in the processing of the image in diffused light to look fordefects.

1. An apparatus for checking a tyre, comprising: a support planeconfigured to receive a tyre; a deformation element configured to applya first force to a first surface portion of said tyre to generate afirst deformed surface portion; a positioning actuator associated withthe deformation element and configured to move said deformation elementtowards and away from said surface of said tyre; and a device includinga camera, a first light source, a second light source, a processing unitand a drive and control unit, wherein said second light source comprisesa first sub-light source and a second sub-light source, said firstsub-light source and said second sub-light source being arranged atopposite sides with respect to an optical plane defined by said camera,the processing unit programmed to: activate said positioning actuator tomove said deformation element towards said tyre to apply a first forceto a first surface portion of said tyre to generate a first deformedsurface portion; and activate said positioning actuator to remove saidfirst force from said first surface portion of said tyre, the drive andcontrol unit programmed to: actuate said first light source toilluminate said first deformed surface portion of said tyre keeping saidsecond light source inactive during said deformation of said firstsurface portion; control said camera to acquire a first image of saidfirst deformed surface portion illuminated by said first light source;actuate said second light source to illuminate a second undeformedsurface portion of said tyre at least partially distinct from said firstsurface portion; and control said camera to acquire a second image ofsaid second undeformed surface portion illuminated by said second lightradiation, the processing unit further programmed to process said firstimage and said second image, to detect possible defects in said firstsurface portion and in said second surface portion of said tyre, thedrive and control unit further programmed to: illuminate the secondundeformed surface portion with the first light source at a first time;illuminate the second undeformed surface portion with the firstsub-light source at a second time different from the first time; andilluminate the second undeformed surface portion with the secondsub-light source at a third time different from the first time and thesecond time.
 2. The apparatus according to claim 1, further comprising arobotic arm coupled with one end to said device.
 3. The apparatusaccording to claim 2, wherein said processing unit is further programmedto move said robotic arm towards said first deformed surface so thatsaid first light source of said device is brought to a distancecomprised between about 25 mm and about 55 mm from said first deformedsurface.
 4. The apparatus according to claim 1, wherein said deformationelement includes a thrusting roller.
 5. The apparatus according to claim4, wherein the thrusting roller is freely rotatable about a thrustingroller axis.
 6. The apparatus according to claim 5, wherein thethrusting roller axis lies on a plane passing through a rotation axis ofthe tyre and through a radial direction of the first deformed surfaceportion.
 7. The apparatus according to claim 6, wherein said thrustingroller axis is positionable at a set angle with the rotation axis ofsaid tyre.
 8. The apparatus according to claim 7, wherein said thrustingroller includes a central portion with increased section along saidthrusting roller axis and an end portion with reduced section along saidthrusting roller axis.
 9. The apparatus according to claim 1, whereinsaid first light source is suitable for emitting diffused lightradiation and said second light source is suitable for emitting grazinglight radiation.